How to Lay Floor Tiles on Concrete?

Concrete slab under the house. That’s the good news walking into most Vancouver Island tile jobs, because a cured slab is about the strongest base a tile ever gets. The catch is the word cured. Skip the checks, and the floor that looked perfect in month one is popping loose or cracking along a hairline by month three.

Can You Tile Directly on Concrete?

Yes, and it’s the most common substrate a tile installer works with on this coast. Concrete is flat, rigid, and doesn’t flex the way a plywood subfloor does, which is exactly what tile wants underneath it. Two conditions have to be true first: the slab needs to be dry, and it needs to be sound, meaning no active cracking or crumbling surface.

Fresh pours are a different animal. New concrete releases moisture as it cures, and mortar bonded to a slab that’s still off-gassing water vapour will fail. Older slabs, the ones under a Nanaimo bungalow built in the seventies or a Comox rancher, come with their own risk: decades of movement, old adhesive residue, maybe a layer of paint from a previous owner’s DIY project. Every one of those gets checked before a single tile goes down.

Check the Slab Before You Buy Tile

Test for Moisture First

Tape a square of plastic sheeting to the concrete, seal every edge, and leave it 24 to 48 hours. Condensation on the underside means the slab is still holding moisture and mortar has no business going on top yet. A cheap pin-type moisture meter does the same job faster and gives an actual reading instead of a yes-or-no.

Older Island homes throw a curveball here that mainland guides don’t mention: slab-on-grade additions and converted sunrooms poured without a proper vapour barrier underneath. Coastal damp works its way up through those slabs year-round, not just after a fresh pour. A slab that tests dry in August can test wet in November. Worth testing more than once if the room in question is an addition rather than the original foundation.

A hygrometer reading tells the same story with a number attached. Anything above roughly 75 percent relative humidity through the slab means hold off, and that reading matters more on a coastal property than it does inland. Rain patterns on this side of the mountains push more groundwater through a slab than a dry Interior climate ever does, so a test that would clear a Kamloops floor can still fail here.

New Concrete Needs Time to Cure

A fresh slab needs roughly one full day of drying time for every millimetre of thickness, up to about 50mm, then closer to two days per millimetre beyond that. A typical 100mm residential slab works out to months, not weeks, before it’s ready for tile. Rushing this step is the single most common reason a brand-new tile floor fails within its first year.

Cracks and Foundation Movement

Hairline cracks under an eighth of an inch can usually be bridged with modified thinset and a crack-isolation membrane. Anything wider, or any crack that’s actively growing, points to foundation movement that needs a proper fix first. Tile has zero flex. Whatever the slab does, the tile and grout do too, just a season or two later.

What to Put Down Before Tiling on Concrete

Bare mortar straight onto bare concrete works on paper. In practice, most jobs get one extra layer first, and which one depends on what the slab is doing.

Uncoupling membrane. A thin polyethylene sheet that separates the tile from the slab below it, so minor movement in the concrete doesn’t transfer straight up into the grout lines. Standard on any floor with hairline cracking history.

Crack-isolation membrane. Thinner than an uncoupling membrane, purpose-built to stop one specific crack from telegraphing through to the tile surface above it.

Cement backer board. Rigid sheets, screwed or thinset down, used more often over plywood than concrete, but sometimes specified where a slab needs extra rigidity under large-format porcelain.

Self-levelling compound. Poured over a slab with dips or low spots before anything else goes down. Skip this on an uneven floor and every tile installer on the crew will feel it in the grout lines within a year.

Primer. Concrete is porous. A primer, usually diluted and rolled on, seals the surface and gives the thinset something consistent to grip. Skipping primer on a dusty or porous slab is asking for weak spots nobody notices until a tile lifts.

Can You Tile Over Painted Concrete?

Short answer, no, not without dealing with the paint first. Thinset needs to bond to concrete, not to a painted film sitting on top of concrete, and paint is exactly the kind of contaminated surface that voids most thinset manufacturer warranties.

The fix is mechanical removal. A grinder with a cup wheel strips paint back to bare, open-pored concrete. Chemical strippers work too, but the slab needs a thorough rinse afterward to clear any residual stripper before mortar goes anywhere near it. Getting every last trace off a textured slab is genuinely hard, and industry guidance from tile consultants is blunt about it: partial paint removal is not close enough. Any paint left under the thinset is a bond that can fail later, even if it holds for the first year or two.

Sunroom conversions on the Island turn this into a recurring call. A patio slab painted years ago, then framed into living space, shows up with rock mixed into the original pour on top of the paint problem. Same answer both times: full paint removal, then a level check, before tile touches the floor.

The scarify-versus-strip decision comes up on nearly every one of these jobs. A cup grinder chews through paint fast and opens the concrete’s pores at the same time, which is exactly what thinset needs to key into. Chemical strippers are slower and messier, better suited to tight corners a grinder can’t reach cleanly. Most crews run both: grinder for the open floor, stripper and a scraper for the edges, then a full rinse and a day to dry before anyone tests moisture again.

Tools and Materials You’ll Need

A notched trowel sized to the tile manufacturer’s spec, a rubber mallet, tile spacers, a wet saw, a margin trowel for mixing, a level, a grout float, and a bucket and sponge cover the install itself. On the materials side: tile with roughly 10 percent extra for cuts and waste, modified thinset mortar, grout, grout sealer if the tile calls for it, and a primer or membrane depending on what the slab check turned up.

How to Lay Tile on Concrete Step by Step

1. Prep and Prime the Slab

Clean, dry, patch, level. That order matters. Sweep and degrease the concrete, confirm it’s dry using the moisture test above, fill any small cracks with a patching compound, then run self-levelling compound if the floor needs it. Prime last, once everything underneath is settled.

2. Plan Your Layout

Snap a chalk line through the centre of the room and dry-lay a row of tile with spacers in place before any mortar goes down. This is where awkward slivers at the wall get caught and adjusted, not after the mortar’s already curing.

3. Mix and Spread the Mortar

Mix modified thinset to a peanut-butter consistency, work in small batches so it doesn’t skin over, and spread it with the notched trowel held at 45 degrees. Cover only as much floor as can be tiled before the mortar starts to set, usually three to four square feet at a time.

4. Set the Tile

Press each tile into the mortar with a slight twist to seat it fully, insert spacers, and check level constantly. Small adjustments are easy while the mortar’s wet. They’re a demolition job once it’s cured.

5. Cut Around the Edges

A wet saw handles straight cuts cleanly. Tile nippers take care of tight spots around pipes, thresholds, and outlets where a saw can’t reach.

6. Grout and Seal

Let the mortar cure a full 24 hours before grouting. Press grout diagonally into the joints with the float, wipe the excess with a damp sponge before it hazes over, and seal once everything’s fully cured if the tile or grout calls for it.

Common Tiling Mistakes on Concrete Floors

Skipping the moisture test tops the list, followed closely by tiling straight over a slab that hasn’t finished curing. After that: ignoring hairline cracks instead of isolating them, using unmodified thinset where modified was specified, and rushing the dry-layout step, which is how a floor ends up with a two-inch sliver of cut tile against the far wall that everyone notices the moment the furniture’s out of the room.

DIY or Call a Tile Installer?

A straightforward small bathroom floor, dry slab, no cracks, no paint to strip, is a realistic weekend DIY project for someone comfortable with a wet saw. Add a crack-isolation membrane, a moisture reading that isn’t clean, or large-format porcelain that doesn’t forgive an uneven mortar bed, and the math changes fast. Large-format tile in particular punishes a lippage problem that a smaller tile would hide.

Cost is usually the first question on a site visit anyway. Materials for a modest floor, thinset, membrane if needed, grout, and the tile itself, run a few hundred dollars before labour enters the conversation. A membrane or self-levelling compound adds to that total fast, sometimes more than the tile itself on a badly uneven slab, which is exactly the kind of detail that never shows up in a rough online estimate. Professional installation adds to that further, but it also removes the risk of a redo, which on a failed concrete substrate means tearing everything back out to bare slab and starting over. That redo costs more than doing it right the first time ever would have. Some of this only gets settled once somebody has seen the actual room, so talk to us first.

Frequently Asked Questions

Can you lay floor tile directly on concrete?

Yes, provided the slab is dry, cured, and free of active cracking. New pours need weeks or months to cure fully. Existing slabs need a moisture test, especially in older Island homes and converted sunrooms.

What do you put down before tiling on a concrete floor?

Depends on the slab’s condition. A clean, dry, level slab with no crack history can take a primer and go straight to thinset. Cracked or moisture-prone floors need an uncoupling or crack-isolation membrane first, and uneven floors need self-levelling compound before anything else.

Will tile stick to painted concrete?

Not reliably, and most thinset warranties exclude painted or contaminated substrates outright. The paint needs mechanical removal, usually with a grinder and cup wheel, back to bare concrete before mortar goes down.

What’s the best flooring to put over concrete?

Tile is one of the strongest options because concrete gives it the rigid, low-flex base it needs. Vinyl and engineered wood can go over concrete too with the right underlayment, but neither handles moisture as well as a properly installed tile floor over a membrane.

What are common tiling mistakes to avoid on a concrete floor?

Skipping the moisture and cure-time checks causes most early failures. After that, unaddressed cracks, wrong mortar type, and rushing the dry layout account for nearly everything else that goes wrong.

Jordan Tile & Stone handles floor tile installation across Campbell River, Courtenay, Comox, Parksville, Nanoose Bay, and Nanaimo, and slab checks are part of every quote before a single tile is ordered. Victoria’s outside the service area, too far south to reach reliably, but everywhere from Campbell River down through Nanaimo is a normal week’s work.

Related Questions

• How to Lay Floor Tiles on Plywood?
• Can I Lay Tile Directly on Concrete?
• Can You Tile Over Tile?
• Can I Tile Over Drywall?

Jordan Tile & Stone

Tile installation and repair across central Vancouver Island: Campbell River, Courtenay, Comox, Oyster Bay, Nanoose Bay, Parksville, Qualicum Beach and Nanaimo.

Phone: (250) 201-3891
Hours: Monday to Sunday, 7:00 am to 6:00 pm
Address: 4423 Patricia Rd, Oyster Bay, BC V9H 1B8